1. Field of the Invention
The present invention relates to a phase detection apparatus and method, and an audio coding apparatus and method, for detecting phases of harmonics components in a sinusoidal wave combine coding or the like.
2. Description of the Prior Art
Various coding methods are known to carry out signal compression utilizing statistical features and human hearing sense characteristics in a time region and frequency region of an audio signal (including a voice signal and an acoustic signal). These coding methods can be briefly classified into time region coding, frequency region coding, and analysis-synthesis coding.
As a high-efficiency coding of an audio signal or the like, there are known sinusoidal coding schemes such as harmonic coding and multi-band excitation (MBE) coding, and sub-band coding (SBC), linear predictive coding (LPC), or discrete cosine transform (DCT), modified DCT (MDCT), fast Fourier transform (FFT), and the like.
In the high-efficiency audio coding using the sinusoidal coding such as the MBE coding, harmonic coding, and sinusoidal transform coding (STC) for an input audio signal or using these sinusoidal coding methods for an input audio signal LPC, information is transmitted on an amplitude or spectrum envelope of each sinusoidal wave (harmonics, higher harmonics) serving as a component of analysis-synthesis. However, no information on phase is transmitted. The phase is calculated during synthesis if necessary.
Accordingly, there is a problem that an audio waveform reproduced after decoding is different from a waveform of the original input audio signal. That is, in order to reproduce the original waveform, it is necessary to detect and transmit phase information of each harmonics (higher harmonics) component for each frame.